This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π–π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graph...

/pdf/noncovalent-functionalization-of-graphene-and-graphene-oxide-49z1h0rufs.pdf

Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications

https://cyberleninka.org/article/n/768408.pdf

Mechanical properties of graphene and graphene-based nanocomposites

This paper gives a comprehensive review about the most recent progress in synthesis, characterization, fundamental understanding, and the performance of graphene and graphene oxide sponges. Practical applications are considered including use in composite materials, as the electrode materials for electrochemical sensors, as absorbers for both gases and liquids, and as electrode materials for devices involved in electrochemical energy storage and conversion. Several advantages of both graphene and graphene oxide sponges such as three dimensional graphene networks, high surface area, high electro/thermo conductivities, high chemical/electrochemical stability, high flexibility and elasticity, and extremely high surface hydrophobicity are emphasized. To facilitate further research and development, the technical challenges are discussed, and several future research directions are also suggested in this paper.

A review of graphene and graphene oxide sponge: material synthesis and applications to energy and the environment

Our understanding of the fundamental structure and bonding of graphene oxide (GO) as well as the scope of its utility have grown tremendously over the past decade. As a result, the pace of research efforts directed toward this carbon material continues to increase. Contemporary application now intersects a variety of disciplines and includes heterogeneous catalysis, flow reactor technologies, biomedicine and biotechnology, polymer composites, energy storage, and chemical sensors. Advances in these areas have been buoyed by improvements in the methods used to synthesize and characterize GO, as well as functionalized derivatives thereof. While the diverse uses of GO have been reviewed previously, herein we provide an overview of some of the most recent and significant developments in the field. A brief overview of GO's synthesis and characterization is also provided as well as several recently proposed structural models. The inherent reactivity of GO is described in the context of catalysis, and the utilization of GO's reactive oxygen groups and carbon framework to prepare functionalized derivatives is also discussed. Finally, we provide an outlook of potential areas where GO, its derivatives, and related materials may be expected to find utility or opportunity for further growth and study.

Harnessing the chemistry of graphene oxide

Graphene is composed of single-atom thick sheets of sp2 bonded carbon atoms that are arranged in a perfect two-dimensional (2D) honeycomb lattice. Because of this structure, graphene is characterized by a number of unique and exceptional structural, optical, and electronic properties.1 Specifically, these extraordinary properties include, but are not limited to, a high planar surface area that is calculated to be 2630 m2 g−1,2 superior mechanical strength with a Young’s modulus of 1100 GPa,3 unparalleled thermal conductivity (5000 W m−1 K−1),4 remarkable electronic properties (e.g., high carrier mobility [10 000 cm2 V−1 s−1] and capacity),5 and alluring optical characteristics (e.g., high opacity [~97.7%] and the ability to quench fluorescence).6 As such, it should come as no surprise that graphene is currently, without any doubt, the most intensively studied material for a wide range of applications that include electronic, energy, and sensing outlets.1c Moreover, because of these unique chemical and physical properties, graphene and graphene-based nanomaterials have attracted increasing interest, and, arguably, hold the greatest promise for implementation into a wide array of bioapplications.7

In the last several years, numerous studies have utilized graphene in bioapplications ranging from the delivery of chemotherapeutics for the treatment of cancer8 to biosensing applications for a host of medical conditions9 and even for the differentiation and imaging of stem cells.10 While promising and exciting, recent reports have demonstrated that the combination of graphene with nanomaterials such as nanoparticles, thereby forming graphene–nanoparticle hybrid structures, offers a number of additional unique physicochemical properties and functions that are both highly desirable and markedly advantageous for bioapplications when compared to the use of either material alone (Figure 1).11 These graphene–nanoparticle hybrid structures are especially alluring because not only do they display the individual properties of the nanoparticles, which can already possess beneficial optical, electronic, magnetic, and structural properties that are unavailable in bulk materials, and of graphene, but they also exhibit additional advantageous and often synergistic properties that greatly augment their potential for bioapplications.




Open in a separate window


Figure 1


Graphene nanoparticle hybrids exist in two forms, as graphene–nanoparticle composites and graphene-encapsulated nanoparticles, and can be used for various bioapplications including biosensors, photothermal therapies, stem cell/tissue engineering, drug/gene delivery, and bioimaging. Panel (A) reprinted with permission from ref 110. Copyright 2012 Wiley. Panel (B) reprinted with permission from ref 211. Copyright 2013 Elsevier. Panel (C) reprinted with permission from ref 244. Copyright 2013 Wiley.

/pdf/design-synthesis-and-characterization-of-graphene-4pt9r1bczt.pdf

Design, Synthesis, and Characterization of Graphene–Nanoparticle Hybrid Materials for Bioapplications

We show that the two-component model of graphene oxide (GO), that is, composed of highly oxidized carbonaceous debris complexed to oxygen functionalized graphene sheets, is a generic feature of the synthesis of GO, independent of oxidant or protocol used. The debris present, roughly one-third by mass, can be removed by a base wash. A number of techniques, including solid state NMR, demonstrate that the properties of the base-washed material are independent of the base used and that it contains similar functional groups to those present in the debris but at a lower concentration. Removal of the oxidation debris cleans the GO, revealing its true monolayer nature and in the process increases the C/O ratio (i.e., a deoxygenation). By contrast, treating GO with hydrazine both removes the debris and reduces (both deoxygenations) the graphene sheets.

Deoxygenation of Graphene Oxide: Reduction or Cleaning?

The treatment of graphene oxide (GO) with potassium thioacetate followed by an aqueous work-up yields a new material via the ring-opening of the epoxide groups. The new material is a thiol-functionalized GO (GO-SH) which is able to undergo further functionalization. Reaction with butyl bromide gives another new material, GO-SBu, which shows significantly enhanced thermal stability compared to both GO and GO-SH. The thiol-functionalized GO material showed a high affinity for gold, as demonstrated by the selective deposition of a high density of gold nanoparticles.

Sulfur‐Functionalized Graphene Oxide by Epoxide Ring‐Opening

Treatment of graphene oxide (GO) with sodium hydroxide separates the material into two components: a colourless, but highly fluorescent, oxidative debris and a darker non-fluorescent material containing the graphene-like sheets. The as-produced GO shows a weak, broad photo-luminescence while the oxidative debris fluoresces more intensely, blue-shifted relative to the as-produced GO, with a dispersive emission profile shifting to lower wavelength as the excitation wavelength is decreased. Such excitation wavelength dependent photoluminescence is characteristic of ensembles of nanometre-sized carbon based fluorophores. By contrast, analysis of the fluorescence as a function of excitation wavelength for as-produced graphene oxide shows a single non-dispersive peak, consistent with broadening of the emission from a single species rather than an ensemble of quantum dots within the graphene sheet.

Helen R. Thomas

Papers

Deoxygenation of Graphene Oxide: Reduction or Cleaning?

Sulfur‐Functionalized Graphene Oxide by Epoxide Ring‐Opening

Identifying the fluorescence of graphene oxide

One-step grafting of polymers to graphene oxide

Concerted reductive coupling of an alkyl chloride at Pt(IV)